Effects of Compost-based Amendments from Sewage Sludge and Food Waste on Sandy Soil and Rosette Bok Choy's Growth

Compost-based organic amendments are an alternative to improve the soil's physical and chemical properties, particularly in soils with poor fertility. These amendments can be derived from natural sources like sewage sludge and food waste, enhancing the soils' structure, water retention, and essential nutrients. This study assessed the effects of adding two composts to sandy soil: sewage sludge (SS) and sewage sludge mixed with food waste (SS + FW). Two controls were used, unamended sandy soil (Ctrl-Soil) and sandy soil mixed with a commercial mineral fertilizer (Ctrl-CF). The soil and the organic amendments were characterized, and all treatments were monitored during a three-week incubation period. Afterward, Rosette Bok Choy plants (Brassica rapa var. rosularis) were cultivated for three weeks. Organic matter (OM) and water content (WC) were proportionally higher as compost rates increased for SS and SS + FW. Significant differences were observed in the 20% and 30% rates compared to the control groups. All rates of SS + FW remarkably increased cation exchange capacity (CEC) compared to the controls, while for SS it was somewhat higher. On the contrary, SS electrical conductivity (EC) was significantly higher in SS 20% and 30% rates. The results showed that SS compost decreased the soil pH and SS + FW increased it with an alkaline tendency. Both composting amendments in their 10% rates improved seed germination over the unamended soil; however, seeds did not germinate in the 20 and 30% treatments, which could imply that these rates are not suitable for the cultivation of Rosette Bok Choy. The best-growing outcomes on roots and shoots were observed in the unamended soil followed by 10% SS + FW. The study findings indicate that organic amendments such as SS + FW are more appropriate for the tested soil and crop compared to the control with mineral fertilizer, which yielded the lowest growth results. The improved growth with organic amendments can be attributed to their ability to increase soil organic matter, whereas mineral fertilizers often contribute to soil degradation over time.